KR20060129835A - Backlight assembly and liquid crystal display apparatus having the same - Google Patents

Abstract

A backlight assembly and an LCD having the same are provided to reduce the brightness of a blue wavelength band and increase the brightness of a red wavelength band, thereby improving the reproduction of color without change of color, by using a diffusing sheet coated with a red fluorescent substance. At least one LED(Light Emitting Diode) generates a white light. A light guiding plate guides the light from the LED. A diffusing sheet(400) is disposed on a light exit surface of the light guiding plate, wherein the diffusing sheet is coated with a red fluorescent substance(420). The red fluorescent substance is applied onto a lower surface of the diffusing sheet, which faces the light guiding plate. The red fluorescent substance is capable of being applied onto an upper surface of the diffusing sheet.

Description

BACKLIGHT ASSEMBLY AND LIQUID CRYSTAL DISPLAY APPARATUS HAVING THE SAME}

1 is an exploded perspective view showing a backlight assembly according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a cross section of the diffusion sheet illustrated in FIG. 1.

3 is a graph showing a spectral change with or without a red phosphor.

4 is a cross-sectional view showing a diffusion sheet according to another embodiment of the present invention.

5 is a cross-sectional view of the light emitting diode shown in FIG. 1.

6 is an exploded perspective view illustrating a liquid crystal display according to an exemplary embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

100: backlight assembly 200: light emitting diode

210: blue chip 220: case

230 molding member 240 yellow phosphor

300: light guide plate 400: diffusion sheet

410: base film 420: red phosphor

430: first bead layer 510: reflective sheet

520: brightness enhancement film 640: second bead layer

700: liquid crystal display 800: display unit

810 liquid crystal display panel 820 driving chip

830: flexible circuit board

The present invention relates to a backlight assembly and a liquid crystal display device having the same, and more particularly, to a backlight assembly and a liquid crystal display device having the same that can improve color reproducibility.

In general, various electronic devices such as mobile communication terminals, digital cameras, notebook computers, and monitors are provided with a display device for displaying an image. Various types of display devices may be used, but a display device having a flat plate shape is mainly used due to the characteristics of an electronic device, and in particular, a liquid crystal display device (LCD) for displaying an image using liquid crystals (Liquid Crystal). Is widely used. The liquid crystal display device is thinner and lighter than other display devices, and has advantages of low driving voltage and low power consumption.

Since the liquid crystal display device is a non-light emitting device that does not emit light by the liquid crystal display panel displaying an image, it requires a backlight assembly for supplying light to the liquid crystal display panel.

The backlight assembly uses a Cold Cathode Fluorescent Lamp (CCFL) or a Light Emitting Diode (LED) as a light source. Cold cathode fluorescent lamps have an advantage in terms of performance compared to the price, but have the disadvantages of being bulky and requiring a high voltage for lighting.

In this regard, the backlight assembly employed in small and medium-sized products such as mobile communication terminals uses a small light emitting diode as a light source due to the characteristics of the product. The light emitting diode has a strong straightness in a specific direction compared to other light sources, and has a form of a point light source having a relatively small light emitting portion. As such, the backlight assembly using the light emitting diode as a light source requires a light guide plate for converting light in the form of a point light source into light in the form of a surface light source, and further requires a diffusion sheet for light diffusion.

Currently, a light emitting diode used in a backlight assembly has a structure in which a yellow phosphor is disposed on a blue chip that generates blue light, thereby implementing white by mixing blue and yellow.

However, since a white light emitting diode having such a structure is based on a blue chip generating blue, the spectrum of the white light emitting diode is centered on a blue chip wavelength band having a relatively short wavelength band, which causes a problem of poor color reproducibility. do.

Accordingly, the present invention has been made in view of such a problem, and the present invention provides a backlight assembly capable of improving color reproducibility by enhancing a long wavelength band.

In addition, the present invention provides a liquid crystal display device having the above-described backlight assembly.

According to an aspect of the present invention, a backlight assembly includes at least one light emitting diode that generates white light, a light guide plate for guiding light from the light emitting diode, and a diffusion sheet disposed on an exit surface of the light guide plate and coated with a red phosphor. It includes.

The red phosphor is coated on a lower surface of the diffusion sheet facing the light guide plate. Alternatively, the red phosphor may be coated on the lower surface and the upper surface of the diffusion sheet.

The red phosphor has a bead shape and has a size of about 5 μm or less.

The light emitting diode includes a blue chip for generating blue light and a yellow phosphor for converting blue light from the blue chip into white light.

The diffusion sheet further includes a first bead layer coated on an upper surface. The first bead layer includes first beads, and the first beads have a size of about 5 μm to about 20 μm.

The diffusion sheet further includes a second bead layer coated on the bottom surface. The second bead layer includes second beads, the second beads having a size of about 5 μm or less.

In addition, the liquid crystal display device according to an aspect of the present invention includes a backlight assembly for supplying light and a liquid crystal display panel for displaying an image using the light supplied from the backlight assembly. The backlight assembly includes at least one light emitting diode for generating white light, a light guide plate for guiding light from the light emitting diode, and a diffusion sheet disposed on an exit surface of the light guide plate and coated with a red phosphor.

According to the backlight assembly and the liquid crystal display having the same, by coating the red phosphor on the diffusion sheet, it is possible to enhance the long wavelength band and improve color reproducibility.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is an exploded perspective view showing a backlight assembly according to an embodiment of the present invention, Figure 2 is a cross-sectional view showing a cross section of the diffusion sheet shown in FIG.

1 and 2, the backlight assembly 100 according to an embodiment of the present invention includes at least one light emitting diode 200, a light guide plate 300, and a diffusion sheet 400.

The light emitting diode 200 is disposed on one side of the light guide plate 300, that is, adjacent to the incident surface 310 to generate white light. Since the light emitting diode 200 emits light within a predetermined angle range, a plurality of light emitting diodes 200 are provided to allow uniform light to be incident on the incident surface 310 of the light guide plate 300. In the present embodiment, the backlight assembly 100 includes three light emitting diodes 200. In contrast, the backlight assembly 100 may include various numbers of light emitting diodes 200 according to the emission angle of the light emitting diodes 200 and the size of the light guide plate 300.

As illustrated in FIG. 5, the light emitting diode 200 includes a blue chip 210 that generates blue light, and further includes a yellow phosphor (not shown) to change blue light generated from the blue chip 210 into white light. 240). Therefore, the light emitting diode 200 emits white light having the center of the blue wavelength band. A detailed description of the light emitting diode 200 will be described later with reference to FIG. 5.

The light guide plate 300 guides a traveling path of the light incident from the light emitting diodes 200 and changes the light in the form of a point light source to the light in the form of a surface light source. The light guide plate 300 is made of a transparent material to minimize the loss of light. The light guide plate 300 is made of, for example, a polymethyl methacrylate (PMMA) material.

The light guide plate 300 extends from an entrance surface 310 facing the light emitting diodes 200, an exit surface 320 extending from one end of the entrance surface 310, and an exit surface 320 extending from the other end of the entrance surface 310. ) And a reflective surface 330 facing away.

A reflective pattern (not shown) for scattering reflection of light is formed on the reflective surface 330 of the light guide plate 300. For example, the reflective pattern consists of a printing pattern or an uneven pattern. Light incident from the light emitting diodes 200 into the light guide plate 300 is scattered and reflected by a reflection pattern, and light exceeding a specific critical angle is emitted through the exit surface 320 or the reflective surface 330 of the light guide plate 300. It is emitted.

The diffusion sheet 400 is disposed on the exit surface 320 of the light guide plate 300. The diffusion sheet 400 includes a base film 410 and a red phosphor 420 coated on the base film 410.

The base film 410 is made of a transparent material for transmitting light. For example, the base film 410 is made of polyethylene terephthalate (PET).

The red phosphor 420 is coated on the bottom surface of the base film 410 facing the light guide plate 300. The red phosphor 420 is fixed to the bottom surface of the base film 410 by the first coating film 422. For example, the first coating film 422 is made of a thermosetting resin or an ultraviolet curable resin cured by heat or ultraviolet rays.

The red phosphor 420 has a bead shape and is irregularly distributed on the base film 410. In this case, the red phosphor 420 has a particle size of about 5 μm or less. The light passing through the diffusion sheet 400 is changed by the red phosphor 420 so that a change in the spectrum in which the blue wavelength band is reduced and the red wavelength band is increased.

3 is a graph showing a spectral change with or without a red phosphor. In the present graph, the first graph G1 shows the spectrum when the diffusion sheet 400 according to the present embodiment is not used, and the second graph G2 shows the diffusion sheet 400 according to the present embodiment. The spectrum of the case is shown.

Referring to FIG. 3, in the first graph G1, the peak wavelengths are shown in the order of blue and yellow under the influence of the blue chip and the yellow phosphor, and the red color has the lowest peak wavelength.

In contrast, in the case of the second graph G2 using the diffusion sheet 400, it can be seen that the peak wavelength of blue is decreased and the peak wavelength of red is increased as compared with the first graph G1.

Therefore, the diffusion sheet 400 coated with the red phosphor 420 improves color reproducibility without changing luminance.

1 and 2, the red phosphor 420 coated on the lower surface of the diffusion sheet 400 may improve a color reproducibility, and may prevent a problem of adhesion between the diffusion sheet 400 and the light guide plate 300. Has That is, the red phosphor 420 keeps the gap between the light guide plate 300 and the diffusion sheet 400 constant, and prevents poor quality such as moiré due to adhesion.

On the other hand, the diffusion sheet 400 further includes a first bead layer 430 formed on the upper surface. The first bead layer 430 has an optical characteristic of diffusing and condensing light passing through the diffusion sheet 400.

The first bead layer 430 includes first beads 432 and a second coating layer 434. The first beads 432 are irregularly distributed on the base film 410, and have a particle size of about 5 μm to about 20 μm. The first beads 432 are made of, for example, a nylon series or polymethyl methacrylate (PMMA). The first beads 432 are fixed to the top surface of the base film 410 by the second coating film 434. For example, the second coating film 434 is made of a thermosetting resin or an ultraviolet curable resin cured by heat or ultraviolet rays.

The backlight assembly 100 further includes a reflection sheet 510 disposed on the reflective surface 330 of the light guide plate 300 and a luminance enhancement film 520 disposed on the diffusion sheet 400.

The reflective sheet 510 reflects the light leaking to the outside through the reflective surface 330 of the light guide plate 300 to the inside of the light guide plate 300 to improve light utilization efficiency. The reflective sheet 510 is made of a material having high light reflectance. For example, the reflective sheet 510 is made of polyethylene terephthalate (PET) or polycarbonate (PC).

The brightness enhancement film 520 improves brightness characteristics by changing a propagation path of light passing through the diffusion sheet 400. The luminance enhancing film 520 may include a prism sheet for focusing the light passing through the diffusion sheet 400 in the front direction. In addition, the brightness enhancement film 520 may include a reflective polarizing film for increasing the brightness of the light.

4 is a cross-sectional view showing a diffusion sheet according to another embodiment of the present invention.

Referring to FIG. 4, the diffusion sheet 600 according to another embodiment includes a base film 610 and a red phosphor 620 coated on the base film 610.

The base film 610 is made of a transparent material for transmitting light. For example, the base film 610 is made of polyethylene terephthalate (PET) material.

The red phosphor 620 is coated on the lower surface and the upper surface of the base film 610. The red phosphor 620 has a bead shape and is irregularly distributed on the lower surface and the upper surface of the base film 610. At this time, the red phosphor 620 has a particle size of about 5㎛ or less. The light passing through the diffusion sheet 600 is changed by the red phosphor 620 to change the spectrum in which the blue wavelength band is reduced and the red wavelength band is increased.

The diffusion sheet 600 further includes a first bead layer 630 formed on an upper surface thereof. The first bead layer 630 has an optical characteristic of diffusing and condensing light passing through the diffusion sheet 600.

The first bead layer 630 includes first beads 632 and a first coating layer 634. The first beads 632 are irregularly distributed on the top surface of the base film 610, and has a particle size of about 5 μm to about 20 μm. The first beads 632 are made of, for example, a nylon series or polymethyl methacrylate (PMMA). The first beads 632 and the red phosphor 620 on the upper surface of the base film 610 are fixed by the first coating layer 634. For example, the first coating film 634 is made of a thermosetting resin or an ultraviolet curable resin cured by heat or ultraviolet rays.

The diffusion sheet 600 further includes a second bead layer 640 formed on the bottom surface. The second bead layer 640 has a function of preventing the adhesion problem between the diffusion sheet 600 and the light guide plate 300.

The second bead layer 640 includes second beads 642 and a second coating layer 644. The second beads 632 are irregularly distributed on the bottom surface of the base film 610 and have a particle size of about 5 μm or less. The second beads 642 are made of, for example, nylon-based or polymethyl methacrylate (PMMA). The second beads 642 and the red phosphor 620 on the lower surface of the base film 610 are fixed by the second coating film 644. For example, the second coating film 644 is made of a thermosetting resin or an ultraviolet curable resin cured by heat or ultraviolet rays.

Meanwhile, in the present embodiment, the red phosphor 620 may be formed only on the top surface of the base film 610.

5 is a cross-sectional view of the light emitting diode shown in FIG. 1.

Referring to FIG. 5, the light emitting diode 200 includes a blue chip 210 generating light, a case 220 accommodating the blue chip 210, and a molding member 230 filled in the case 220. .

The blue chip 210 is disposed inside the case 220 and generates light of a blue wavelength band in response to power applied from the outside.

The case 220 has a funnel shape so that light generated from the blue chip 210 can be spread out at a wide angle. The case 220 is formed of an insulating material to protect the blue chip 210. For example, the case 220 is formed of a polymer or a ceramic material. A reflection layer (not shown) for reflecting light may be formed on an inner surface of the case 220.

The molding member 230 is filled in the case 220 to protect the blue chip 210. The molding member 230 is made of a resin material such as silicon.

The molding member 230 includes a yellow phosphor 240 for converting blue light generated from the blue chip 210 into white light. For example, the yellow phosphor 240 is made of Yttrium Aluminum Garnet (YAG) phosphor. That is, the blue light generated from the blue chip 210 reacts with the yellow phosphor 240 to implement white light. Therefore, the light emitting diode 200 emits white light having the center of the blue wavelength band.

6 is an exploded perspective view illustrating a liquid crystal display according to an exemplary embodiment of the present invention.

Referring to FIG. 6, the liquid crystal display 700 according to an exemplary embodiment of the present invention may include a backlight unit 100 for supplying light and a display unit for displaying an image using light supplied from the backlight assembly 100. 800).

The backlight assembly 100 may have the same configuration as the embodiments shown in FIGS. 1 to 5. Therefore, the same reference numerals are used, and detailed description thereof will be omitted.

The display unit 800 includes a liquid crystal display panel 810 for displaying an image, a driving chip 820 for driving the liquid crystal display panel 810, and a flexible circuit board for supplying various control signals to the liquid crystal display panel 810. 830.

The liquid crystal display panel 810 includes a first substrate 812, a second substrate 814 coupled to face the first substrate 812, and a liquid crystal interposed between the first substrate 812 and the second substrate 814. Layer (not shown).

The first substrate 812 is a TFT substrate in which a thin film transistor (hereinafter, referred to as TFT) as a switching element is formed in a matrix form. For example, the first substrate 812 is made of a transparent glass material for light transmission. A data line and a gate line are respectively connected to the source terminal and the gate terminal of the TFTs, and a pixel electrode made of a transparent conductive material is connected to the drain terminal.

The second substrate 814 is a color filter substrate in which RGB pixels for realizing color are formed in a thin film form. The second substrate 814 is made of, for example, a transparent glass material. The common electrode made of a transparent conductive material is formed on the second substrate 814.

In the liquid crystal display panel 810 having such a configuration, when power is applied to the gate terminal of the TFT and the TFT is turned on, an electric field is formed between the pixel electrode and the common electrode. By the electric field, the arrangement of the liquid crystal molecules of the liquid crystal layer interposed between the first substrate 812 and the second substrate 814 is changed, and the transmittance of light supplied from the backlight assembly 100 is changed according to the arrangement of the liquid crystal molecules. The image is changed to display an image of a desired gray scale.

The driving chip 820 is formed on the first substrate 812. The driving chip 820 generates a driving signal for driving the liquid crystal display panel 810 in response to various control signals applied through the flexible circuit board 830. The driving signal generated from the driving chip 820 is applied to the gate line and the data line of the first substrate 812 to drive the liquid crystal display panel 810.

The flexible circuit board 830 is connected to one side of the first substrate 812 on which the driving chip 820 is mounted. The flexible circuit board 830 includes a timing controller for controlling driving timing of the driving chip 820, a memory for storing data signals, and the like. The flexible circuit board 830 is electrically connected to the first substrate 812 through, for example, an anisotropic conductive film (ACF).

According to such a backlight assembly and a liquid crystal display device having the same, by using a diffusion sheet coated with a red phosphor, the emission luminance of the blue wavelength band of the emitted light is reduced, and the emission luminance of the red wavelength band is increased. Thus, color reproducibility is improved without changing the luminance.

In the detailed description of the present invention described above with reference to the preferred embodiments of the present invention, those skilled in the art or those skilled in the art having ordinary skill in the art will be described in the claims to be described later It will be understood that various modifications and variations can be made in the present invention without departing from the scope of the present invention.

Claims (14)

At least one light emitting diode for generating white light; A light guide plate for guiding light from the light emitting diode; And And a diffusion sheet disposed on an exit surface of the light guide plate and coated with a red phosphor. The backlight assembly of claim 1, wherein the red phosphor is coated on a bottom surface of the diffusion sheet facing the light guide plate. The backlight assembly of claim 1, wherein the red phosphor is coated on a lower surface and an upper surface of the diffusion sheet. The backlight assembly of claim 1, wherein the red phosphor has a bead shape. The backlight assembly of claim 4, wherein the red phosphor has a size of 5 μm or less. The method of claim 1, wherein the light emitting diode A blue chip for generating blue light; And And a yellow phosphor for converting blue light from the blue chip to white. The backlight assembly of claim 1, wherein the diffusion sheet further comprises a first bead layer coated on an upper surface thereof. The backlight assembly of claim 7, wherein the first bead layer includes first beads, and the first beads have a size of about 5 μm to about 20 μm. The backlight assembly of claim 7, wherein the diffusion sheet further comprises a second bead layer coated on a bottom surface thereof. The backlight assembly of claim 9, wherein the second bead layer comprises second beads, the second beads having a size of 5 μm or less. The method of claim 1, A reflection sheet disposed on a reflection surface of the light guide plate; And The backlight assembly further comprises a brightness enhancement film disposed on the diffusion sheet. A backlight assembly for supplying light; And It includes a liquid crystal display panel for displaying an image using the light supplied from the backlight assembly, The backlight assembly At least one light emitting diode for generating white light; A light guide plate for guiding light from the light emitting diode; And And a diffusion sheet disposed on the exit surface of the light guide plate and coated with a red phosphor. The liquid crystal display of claim 12, wherein the red phosphor is coated on at least one of a lower surface and an upper surface of the diffusion sheet. The liquid crystal display device according to claim 12, wherein the red phosphor has a bead shape and has a size of 5 µm or less.

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